tipc: make macro tipc_wait_for_cond() smp safe

The macro tipc_wait_for_cond() is embedding the macro sk_wait_event()
to fulfil its task. The latter, in turn, is evaluating the stated
condition outside the socket lock context. This is problematic if
the condition is accessing non-trivial data structures which may be
altered by incoming interrupts, as is the case with the cong_links()
linked list, used by socket to keep track of the current set of
congested links. We sometimes see crashes when this list is accessed
by a condition function at the same time as a SOCK_WAKEUP interrupt
is removing an element from the list.

We fix this by expanding selected parts of sk_wait_event() into the
outer macro, while ensuring that all evaluations of a given condition
are performed under socket lock protection.

Fixes: commit 365ad353 ("tipc: reduce risk of user starvation during link congestion")
Reviewed-by: Parthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/socket.c

@@ -362,22 +362,22 @@ static int tipc_sk_sock_err(struct socket *sock, long *timeout)
 	return 0;
 }
 
-#define tipc_wait_for_cond(sock_, timeout_, condition_)			\
+#define tipc_wait_for_cond(sock_, timeo_, condition_)			       \
 ({                                                                             \
-	int rc_ = 0;							\
-	int done_ = 0;							\
+	struct sock *sk_;						       \
+	int rc_;							       \
 									       \
-	while (!(condition_) && !done_) {				\
-		struct sock *sk_ = sock->sk;				\
+	while ((rc_ = !(condition_))) {					       \
 		DEFINE_WAIT_FUNC(wait_, woken_wake_function);	               \
-									\
-		rc_ = tipc_sk_sock_err(sock_, timeout_);		\
+		sk_ = (sock_)->sk;					       \
+		rc_ = tipc_sk_sock_err((sock_), timeo_);		       \
 		if (rc_)						       \
 			break;						       \
-		prepare_to_wait(sk_sleep(sk_), &wait_,			\
-				TASK_INTERRUPTIBLE);			\
-		done_ = sk_wait_event(sk_, timeout_,			\
-				      (condition_), &wait_);		\
+		prepare_to_wait(sk_sleep(sk_), &wait_, TASK_INTERRUPTIBLE);    \
+		release_sock(sk_);					       \
+		*(timeo_) = wait_woken(&wait_, TASK_INTERRUPTIBLE, *(timeo_)); \
+		sched_annotate_sleep();				               \
+		lock_sock(sk_);						       \
 		remove_wait_queue(sk_sleep(sk_), &wait_);		       \
 	}								       \
 	rc_;								       \